irb(main):011:0> a = true
  =>true
irb(main):012:0> b = false
  =>false
irb(main):013:0> 5.times { |x|
irb(main):014:1*             puts x
irb(main):015:1>   } if a
0
1
2
3
4
  =>5
irb(main):016:0> 5.times { |x|
irb(main):017:1*             puts x
irb(main):018:1>   } if b
  =>nil
irb(main):019:0>